
Add getElement and getDomHelper to goog.ui.Dialog.ButtonSet, copied from
goog.ui.Component for forward compat.

I'm writing a dialog that subclasses ButtonSet for custom rendering, and
needs access to those fields. I noticed several TODOs to refactor ButtonSet
into a goog.ui.Component, so adding some of the methods early seems ok.

I haven't changed the tests since they're both straight getters, but let me
know if I should add something anyway.

R=gboyer,pupius
DELTA=20  (20 added, 0 deleted, 0 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=1514


git-svn-id: 35241bd708fe29f1f6c7a4322d322e99ff93b95e@867 0b95b8e8-c90f-11de-9d4f-f947ee5921c8

neilrahilly/closure-library,jarib/google-closure-library,homer6/google-closure-library,rethinkdb/google-closure-library,rethinkdb/google-closure-library,prop/closure-library,neilrahilly/closure-library,prop/closure-library,Kuniwak/google-closure-library-jsdoc,rethinkdb/google-closure-library,thinkfuse/google-closure,Kuniwak/google-closure-library-jsdoc,homer6/google-closure-library,thinkfuse/google-closure,prop/closure-library,KgDesignes/closure-library,knutwalker/google-closure-library,KgDesignes/closure-library,neilrahilly/closure-library,jarib/google-closure-library,KgDesignes/closure-library,thinkfuse/google-closure,knutwalker/google-closure-library,homer6/google-closure-library